Non-Exhaust Automotive Pollution
Cars are well known for their tail pipe pollution. Great efforts have been made to reduce such. But there are other sources associated with vehicles that are not normally considered. Vehicle exhausts are responsible for only a third of traffic pollution, according to new research. The study, published in Atmospheric Environment, says nearly half of air pollution from road traffic is due to non-exhaust sources such as brake wear, road surface wear, and particles whipped up from the road by passing vehicles. Professor Ranjeet Sokhi, of the University of Hertfordshire, who led the study, is calling for greater control of non-exhaust pollution.
"In terms of mass, non-exhaust sources can be more important than exhaust fumes, but legislative control has focused on exhaust emissions," he says.
"As exhaust regulations become stricter, non-exhaust sources become proportionately more important. Continuing to control exhaust emissions alone may not be enough to achieve legal air-quality standards."
The non-exhaust pollution discussed is particulate matter. Everything solid can be broken into smaller pieces. These sources include: Tire wear, brake wear, clutch wear, and road wear or deterioration. In addition other particulates matter is moved by the passage of the vehicle or the wind. Most of this particulate matter will be large particles that will settle quickly some will be smaller PM 10 or less particles.
The team took air samples from the Hatfield Tunnel on the A1 Motorway in Hertfordshire in England. They were interested in airborne pollution particles less than 10 millionths of a meter across.
Pollution particles of that size, known as PM10, are linked with long-term health problems, including heart disease.
"Other studies have looked at non-exhaust components of PM10, but those have mostly been done in open-air locations," explains Sokhi. "We wanted to look at them in a more controlled environment, where the influence of the weather could be significantly reduced."
"The Hatfield tunnel provided an ideal laboratory; you are protected from the elements and it confines the airborne particles, making it easier to collect sufficient material for analysis."
Back in the lab, samples were separated out into their chemical components. By analysing these, scientists were able to calculate where up to 82% of the pollution in the samples had originated from.
Oil and diesel exhausts (direct from the tail pipe) are responsible for only 33 per cent of the particles. 27 per cent are disturbed by the movement of the vehicle from the road, while brake and road surface deterioration account for 11 per cent.
In 2010, Transport for London began spraying a calcite glue solution onto roads, in an attempt to stick potential air borne particulates to the road surface. But a recent study by scientists at King's College London has questioned the effectiveness of the scheme.
"It is important to recognize that controlling non-exhaust emissions is more difficult; a number of different approaches might be needed," says Sokhi.
"Where possible, new technologies and other pollution reduction options should be investigated. These might include, for example, new materials for tires and brakes and different methods for constructing road surfaces."
For further information see Non-Exhaust Pollution.
Road Dust image via Alaska DEC.